If you want to add a trooper to the squad, stick a trooper into the level, and change both bCanbesquadmember and bOfSquadInterest to true. Do NOT change bCanPreformSquadCommands to true, or you game will crash every time your order the squad to do something.

Go to the Actor Classes viewer
Go to Pawn - CTPawn - Republic - CloneTrooper and select CloneTrooperTM
Right-click the floor next to where your squad starts and choose Add CloneTrooperTM Here
Double-click the trooper to bring up the CloneTrooperTM# Properites window, and click on AI
Set both bCanBeSquadMember, and bOfSquadInterest to true
Save, and boot up the level.